Acoustic resonators are used in rotating machinery, such as turbomachines, to reduce pressure pulsation, vibrations, and noise. The use of acoustic resonators provides several advantages, including lowering noise emissions. One type of resonator is known as a Helmholtz resonator, which typically includes a chamber with a throat oriented toward the acoustical source. Such Helmholtz resonators can be positioned in arrays within the machinery, for example, as acoustic liners positioned proximal the flowpath, thereby reducing the acoustical energy emanating therefrom.
Conventional Helmholtz resonators, however, are typically effective over a relatively narrow frequency band, for example, about one octave. Accordingly, multi-degree of freedom resonator arrays have been developed to provide effective attenuation of a broader frequency band of noise and vibration. Passive multi-degree of freedom arrays are generally constructed from multiple layers of acoustic liners. As such, acoustical energy passes through two or more sets of resonators, thereby attenuating the noise and vibration over a broader frequency band. Active multi-degree of freedom arrays have been proposed that actively alter in geometry, such as electromechanical Helmholtz resonators, with results similar to passive arrays.
These multi-degree of freedom resonator arrays, while generally suitable in a variety of applications, are often expensive to manufacture, bulky, and, especially in the case of active resonators, can add complexity to the system, thereby increasing the chances for system failure. What is needed is a multi-degree of freedom resonator array that does not suffer from these drawbacks and/or others.